In recent years, large-sized liquid crystal display panels have been under development. A large-sized liquid crystal display panel may exhibit symptoms of a partial difference in luminance within the liquid crystal display panel when, in an inspecting step at a manufacturing stage, the liquid crystal display panel displays a screen image for inspection (so-called “solid screen image”) of the same low-tone color (hereinafter such symptoms being referred to as “luminance unevenness”).
The occurrence of such luminance unevenness in a large-sized panel is due to the fact that production tolerance within a liquid crystal display panel, such as variations in line width and film thickness within a TFT substrate, tends to occur in a plane of a single liquid crystal display panel and variations in gradation due to TFT characteristics and/or parasitic capacitances on wires occur with an in-plane distribution. In particular, a panel based on divisional driving may prominently exhibit luminance unevenness.
Patent Literature 1 discloses dividing a display panel into a plurality of regions and controlling a gate pulse width for each of the regions divided from each other, in order that the display panel is prevented from exhibiting luminance unevenness.
FIG. 7 is a diagram schematically showing the locations of a display panel 100, a scanning driver 120, and a signal driver 130 as described in Patent Literature 1.
The display panel 100 has its display region divided into three regions A, B, and C arranged in the order of decreasing distance from the scanning driver 120 along a column-wise direction. The scanning driver 120 applies scanning signals G1 to Gm to scanning lines of the region A, applies scanning signals Gm+1 to G2m to scanning lines of the region B, and applies scanning signals G2m+1 to G3m to scanning lines of the region C.
FIG. 8 is a diagram showing the waveforms of the scanning signals G that are applied to the scanning lines of the display panel 100.
As shown in FIG. 8, the pulse width Wb of each of the scanning signals Gm+1 to G2 that are applied to the scanning lines of the region B is smaller than the pulse width Wa of each of the scanning signals G1 to Gm that are applied to the scanning lines of the region A. Furthermore, the pulse width Wc of each of the scanning signals G2m+1 to G3 that are applied to the scanning lines of the region C is smaller than the pulse width Wb of each of the scanning signals Gm+1 to G2 that are applied to the scanning lines of the region B.
FIG. 9 is a diagram showing examples of waveforms of the scanning signals G that are applied to each separate pixel of the display panel 100.
FIG. 9 shows the waveform of a signal that is applied to each scanning line Lg of the region A, the waveform of a signal that is applied to each scanning line Lg of the region B, and the waveform of a signal that is applied to each scanning line Lg of the region C, starting from the top. It should be noted that each of the dotted lines indicates the waveform of a scanning signal G at the point in time where the scanning signal G was outputted from the scanning driver 120.
By thus setting, for each of the regions A, B, and C into which the display panel 100 has been divided, the pulse width Wa, Wb, or Wc of each of the scanning signals G that are applied to the scanning lines of that region, periods of time ta, tb, and tc during which the TFT of each separate display pixel of the display panel 100 carries out an ON operation are made substantially equal.
This causes display signal voltages to be applied to each separate display pixel for substantially uniform periods of time, thus preventing deterioration in image quality of a display image from occurring due to a biased wiring load.
Patent Literature 2 discloses a liquid crystal display device which forms, in at least either of a rising or a falling edge portion of a pulse wave that drives a signal line or a scanning line, a region of a level value that is lower than a peak value of the pulse wave. This prevents display unevenness from occurring due to a distortion of a pulse wave along with inversion or the like.
Patent Literature 3 discloses a liquid crystal display device which, by inclining the waveform of a falling edge portion of a scanning signal, makes it harder for the waveform of the falling edge portion of the scanning signal to be distorted.
FIG. 10 is a diagram showing a configuration of the liquid crystal display device of Patent Literature 3.
As shown in FIG. 10, the liquid crystal display device 400 includes a liquid crystal display panel 401, picture signal lines 5400, scanning signal lines G400, picture signal line driving circuits 200-1 and 200-2, scanning signal line driving circuits 300-1 to 300-3, and a control circuit 600.
FIG. 11 is a diagram showing the waveforms of signals that are outputted from the picture signal line driving circuits 200-1 and 200-2, the scanning signal line driving circuits 300-1 to 300-3, and the control circuit 600.
FIG. 12 is a diagram showing a configuration of the scanning signal line driving circuits 300-1 to 300-3.
The control circuit 600 generates a clock signal GCK 400 and a periodic signal Stc400 in accordance with which the picture signal line driving circuits 200-1 and 200-2 and the scanning signal line driving circuits 300-1 to 300-3 operate.
Each of the picture signal line driving circuits 200-1 and 200-2 uses the clock signal GCK400 to apply, to the picture signal lines 5400, a picture signal supplied from an outside source. Each of the scanning signal line driving circuits 300-1 to 300-3 uses the clock signal GCK400 and the periodic signal Stc400 to generate a scanning signal VG400 and apply it to the scanning signal lines G400.
The scanning signal line driving circuit 300-1 includes an internal modulation section 310-1 and a scanning signal line driving section 315-1. The internal modulation section 310-1 generates a driving signal VM100 in accordance with a potential Vgh and an intermediate signal Vct400. The scanning signal line driving section 315-1 generates a scanning signal VG400 in accordance with the driving signal VM400 generated by the internal modulation section 310-1.
The inclination of a falling edge portion of the scanning signal VG400 makes it harder for a falling edge of the scanning signal VG400 to be distorted, thus preventing deterioration in display quality.
Furthermore, the scanning signal line driving circuits 300-1 to 300-3 have their internal wires connected to one another via a signal wire 305. This allows averaging of the waveforms of the driving signals VM100 to 300 that are applied to the internal wires, respectively. That is, this allows the driving signals VM100 to VM300 to have their respective sloping parts to be substantially equal in inclination to one another. This prevents display quality from varying from one display area to another.